.wrapper {
  padding: 16px;
}

.box_2 {
  width: 100px;
  height: 100px;
  border-radius: 20px;
  background-color: aqua;
  box-shadow: -1px -1px black;
  animation: shadow2 5s infinite;
}
@keyframes shadow2 {
  50%{
    box-shadow: -15px -15px lightblue;
  }
}